Typically, a bicycle wheel includes a rim, on which a tire, a hub, and a plurality of spokes extending between the rim and the hub are mounted.
Between the rim and the tire, an air chamber can be inserted which, once inflated through a suitable inflation valve, brings the tire into the desired operative configuration. The inflation valve is typically associated with a thickened portion of the air chamber.
Amongst the various types of bicycle wheels, use of the type known as “tubeless,” i.e. without an air chamber, is now widespread. In tubeless wheels, the tire is mounted airtight on the rim, so as to form an airtight annular area in which pressurized air is introduced through an inflation valve associated with the rim at a suitable hole formed in the rim.
The airtight annular area of tubeless wheels is defined by an inner surface of the tire and an outer surface of the rim. In particular, the rim comprises a radially outer portion provided with an annular bottom wall, or upper bridge, and with a pair of annular side walls, or fins, extending radially outwards from the upper bridge; such fins hold the tire, in a final assembled configuration, against the thrust of the pressurized air, achieving an airtight coupling between tire and rim.
The outer surface of the rim that defines the airtight annular area is therefore defined by the radially outer surface of the upper bridge of the rim and the axially inner surfaces of the fins.
The hole for the inflation valve is formed in the upper bridge of the rim. The upper bridge has no further holes. In particular, there are no holes for the assembly of the spokes of the wheel; such holes are instead generally provided in a radially inner portion of the rim. In those cases in which the holes for the assembly of the spokes are formed in the upper bridge of the rim, they are suitably sealed, for example through a rubber band.
The inflation valve includes a stem adapted to pass through the hole formed in the upper bridge of the rim, and a head which is widened with respect to the stem. The head is typically made from elastic material.
The head of the inflation valve is adapted to abut the radially outer surface of the upper bridge of the rim so as to prevent the stem from slipping out from the hole in a radially inward direction with respect to the rim. A ring nut is screwed onto the stem and abuts a radially inner surface of the rim, so as to keep the stem from slipping in the radially outward direction with respect to the rim. In addition, the screwing of the ring nut allows the head made from elastic material to be kept in abutment with a surface portion around the hole in which the stem is inserted, achieving the desired seal against the leakage of air from the hole.
In a significant number of tubeless wheels of the type described above there are problems of deflation; on the other hand, other absolutely identical wheels do not have this problem.
In order to repair the tubeless wheel it is necessary to replace the tire. However, it is not very practical for a cyclist to transport spare tires. For this reason, the cyclist generally prefers, in the case of a puncture to the tire, to insert an air chamber between rim and tire, thus transforming the tubeless wheel into a normal wheel with an air chamber.
The presence of the air chamber, however, has the same drawback already present in normal wheels with an air chamber, i.e. the need to establish an optimal coupling between rim, air chamber and tire. Such an optimal coupling is difficult to achieve in practice, for which reason all wheels provided with an air chamber (both the tubeless ones in which the air chamber is inserted following a puncture and the normal ones that are provided with the air chamber from the beginning), in practice, have a operating efficiency lower than that of the tubeless wheels without an air chamber.